The use of image guided surgical navigation systems for assisting surgeons in performing delicate surgery has become more common. Typical surgical navigation systems utilize specially developed tools that include built in tracking devices so that the surgeon can see the position of the surgical tool overlaid on a monitor that shows a preoperative image or an intraoperative image. The preoperative images are typically prepared using well-known preoperative scanning techniques, such as MRI or CT scans. The intraoperative images can be prepared using flouroscope, low level x-ray and similar devices. The tracking devices typically include multiple optical emitters, such as LED's, that can be detected by the surgical navigation system. From the position of the emitters, the surgical navigation system can determine the position and/or orientation of the surgical tool.
As used in this specification, the term position means the coordinates of the tip of the surgical tool in three-dimensional space, the x, y, z or Cartesian coordinates, relative to the surgical navigation system. The term orientation means the pitch, roll, and yaw of the surgical tool. When both the position and the orientation of a surgical tool are defined, the absolute position of that surgical tool is known to the surgical navigation system.
In order for a surgeon to use a surgical tool without a built in tracking device with a surgical navigation system, a universal tracking device must be attached to the surgical tool. The universal tracking device and the surgical tool combination must be calibrated so that the surgical navigation system knows the relation between tip of the surgical tool and the position of the tracking device. Surgical tools with the attached universal tracking device can be calibrated and then tracked. If the tracking device and surgical tool have been calibrated relative to the surgical navigation system so that only the position of the tip of the surgical tool is known to the surgical navigation system, then only the position of the tip but not the orientation of the surgical tool can be tracked by the system. Because the exact path the surgeon will take during a particular surgical procedure is very important, it is preferable to know both the position and orientation of the surgical tools used during that procedure so that the surgical tools can be completely represented on the monitor of typical surgical navigation systems.
In order to provide both position and orientation data for the combination of the surgical tool and the attached universal tracking device, both the position and orientation for each surgical tool and tracking device combination must be calibrated. Typical prior calibration devices have been described in U.S. Pat. Nos. 5,987,960, 5,921,992 and 6,306,126. Each of these calibration devices utilizes the principal of constraining the axis of the surgical tool in a plane perpendicular to a base of the calibration device. Because the position of the base of the calibration device and the position of the axis of the surgical tool are known relative to optical tracking elements contained on the calibration device, the surgical navigation system can calculate the position and the orientation for the particular surgical tool and the tracking device combination. Thereafter, that surgical tool and tracking device combination can be completely tracked by the surgical navigation system.